Controlled displacement sewage air lift station

ABSTRACT

An air lift station for lifting sewage from a sewage receiver tank in discrete ejection cycles by forced air, is provided with means for maintaining constant the quantity of air injected into a sewage receiving tank from an accumulator tank. The station provides improved reliability of the air compressor motor circuit and improved overall lift station efficiency. Specifically, during each timed ejection cycle, the air is injected at the same constant pressure.

United States Patent Chamberlain Oct. 28, 1975 1 CONTROLLED DISPLACEMENTSEWAGE 3,322,306 5/1967 Munderich 222/373 x I LIFT STATION 3,393,6447/1968 Boswell 137/209 X 3,537,472 11/1970 Yulio 417/138 X [76]Inventor: Jess L. Chamberlain, 1482 Antomette, Clncmnati, Ohio 45230Primary Examiner Robert Reeves [22] Filed: Jan. 18, 1971 AssistantExaminer-Hadd Lane [2]] App O 107 294 Attorney, Agent, 07" Firm-Wood,Herron & Evans [57] ABSTRACT [52] US. Cl 417/138; 222/373 51 Im. C1.F04F 1/06 1 ftmg sewage from a Sewage 58 Field of Search 137/13, 209,386, 395; tank 3 discr-ete by forced is 222/373; 302/14; 417/138, 145,146,141 1 f l 9 mamammg l i the quant1ty of an m ected into a sewagerece1v1ng tank [56] References Cited from an accumulator tank. Thestation provides imd bTt UNITED STATES PATENTS 5137115276558111121211135ZiELEJJZfEiZZET 1,253,558 1/1918 Aikman 417/145 X cally,during each timed ejection cycle, the air is in St gg 22 /373 X jectedat the same constant pressure. a or 3,203,637 9/1965 Heick 222/1373 X 5Claims, 1 Drawing Figure A3 01/2 07 A i ZfVfL 7K5 may/m E/Yrs /0 57 75224 2 2 t t /a ZZZ 17a 22] a 24 u AM 6fl\ e 4/ I 1 CONTROLLEDDISPLACEMENTSEWAGE AIR LIFT STATION The present invention relates to sewage handlingapparatus,j and,- more particularly, to low maintenance, high efficiencysewage lift stations of the air lift type.

BACKGROUND OF THE INVENTION I Sewage systems, particularly inmetropolitan areas, usually employ one or more centrally located sewagetreatment facilities. These facilities are located at a relatively lowelevation, and sewer lines from the surrounding community conduct thesewage on a gravity flow basis to these facilities. The normal flow ofsewage in these sewers requires that a certain grade or incline bemaintained so that the sewage can flow with sufficient velocity so thatthe sewers can accommodate the requirements of the community.Frequently, however,

the outlying areas around a community are of such distancesandelevations that an adequate incline cannot be maintained to thecentral facility, and in such cases it is necessary to employ sewagelift stations to lift the sewage from a low elevation to a higherelevation so that it can continue to flow under the influence of gravityto the central treatment facility.

Normally, it is not possible to employ conventional pumps for thepurpose of the sewage lift station. This is primarily due to theconsistency of the sewage and the volume flow rate of the sewage whichis normally encountered. For example, the sewage which is received mustbe expected to contain suspended solid material which many mechanicalpumps cannot handle. Furthermore, the particles of solid material may beseveral inches in diameter requiring sewer line diameters of at least 4inches and usually greater at the ports of the pumps. With lines of suchsize, the pumps used will have an inherently large displacement, andwith most mechanical pumps of such size, it would be rare if the flowrate of the sewage into a given lift station were sufficiently high toallow the continuous operation of such pumps to lift the sewage.Therefore, it is essential for most situations to use pumps that areoperable on an intermittent basis. Such intermittently operable pumpsare provided with sewage receiving tanks which can accumulate asufficient amount of sewage to allow for the efficient operation of thepump in discrete ejection cycles in transferring the sewage to a higherelevation.

Mechanical pumps which are suitable in handling line diameters of thismagnitude are inordinately expensive and inefficient for intermittentoperation. Thus, the general approach taken in the art has been toemploy, pneumatic lift stations which accumulate sewvage in a receivertank until the receiver tank is filled used, to directly supply thisair. In many systems two compressors are used to increase reliability incase one should fail. For more efficient operation, however,

manyisystems'employ an air accumulator. These systems operate thecompressor intermittently to charge the accumulator toa high pressure.Air then intermittently emitted from the accumulator into the receivertank to eject the sewage from the receiver tank during ejection cycles,which may occur either between or during the compressor cycles.

While such systems of the prior art have been usually adequate whenconsidered from a dynamic and fluid handling point of view, such systemshave been inefficient in their use of electrical power to operate thecompressors, and, most importantly, these systems of the prior art haveplaced an extremely heavy demand upon the durability of the compressormotors and the starter switches which energize them. Such heavy demandhas resulted in frequent breakdowns and malfunctions in the electricalequipment, high maintenance costs, and added capital expense foremergency backup equipment to reduce the downtime of the sewage liftstations.

It has been found that the maintenance required to service thecompressor motors and the motor starters is directly proportional to thenumber of times that the motor is required to start and stop. Thismaintenance is manifested in a wearing of the contacts of the starterswitches and in an accelerated deterioration of the motor windings.

This problem is particularly acute when one-phase motors are used, butit is also significant when threephase motors are employed. This effecton three-phase motors, however, is not as pronounced as in the case ofone-phase motors due to the inherent suitability of three-phase motorsto frequent start and stop operations. Therefore three-phase motors arenormally used whenever three-phase power has been available. In manylocations, however, three-phase power is not available and one-phasepower must be employed.

SUMMARY OF THE INVENTION Accordingly, it is a primary objective of thepresent invention to provide an improved sewage lift station in whichthe electrical power system requires less maintenance and has greaterreliability that has been provided by lift stations of the prior art,and which has a good overall operational efficiency.

It is another object of the present invention to provide a sewage airlift station of the type having an air accumulator to supply motivefluid wherein the motive air is conserved to the greater extent than inthe prior art systems, thereby reducing the requirement tofrequently'charge the air accumulator through frequent intermittentoperation of a compressor motor, in relation to the ejection cyclefrequency.

The present invention is predicated in part upon the concept of reducingthe frequency of compressor motor cycles in relation to the: ejectioncycle frequency by metering the air used in each ejection cycle so as tosupply a constant quantity of air in each ejection cycle. Since saidlift stations are usually moving sewage against a constant hydro-staticback pressure, a constant quantity of air provides :a constant fluiddisplacement in each sewage ejection cycle. One specific waycontemplated by the present invention of metering the quantity of air isto regulate the air from the air accumulator on a time basis, and moreparticularly by controlling the pressure-time relationship of theinjected air in a sewage ejection cycle so as to provide a constantsewage displacement, from cycle to cycle.

More particularly, the specific embodiment of the present inventionprovides the injection of air under constant pressure from cycle tocycle for ejection cycles of constant time duration.

A primary advantage of the present invention is in the significantreduction in the maintenance required of the lift station, particularlyof the compressor motors and the motor starter circuits. Furthermore,the present invention allows the use of electrical components of reducedcost and durability. The present invention has particularly increasedthe ratio of ejection cycles per compressor motor starts. For example,by operating conventional lift stations in accordance with the presentinvention, this ratio has been increased by up to factors of 30, in somecases.

When higher pressures were used, prior to the present invention, it wasfound that much more air was used in the first ejection cycle after acompressor cycle, than in the last ejection cycle before a compressorcycle. This has been primarily due to the fact that with fixed timeduration ejection cycles, more air was used at high pressure than at lowpressure. Thus, a given ejection cycle which is adequate for lowpressures has resulted in a considerable use of excessive air at thehigher pres sures. This factor has placed a practical upper limit on theoverpressurization of the air accumulator.

Another advantage of the present invention. is that the electrical powerrequired to operate the lift station is reduced, increasing materiallythe power efficiency of the station.

Another and important advantage of the present in vention is that, inaddition to the advantages manifested to the electrical system as setforth above, the overall operating efficiency of the system is increasedin an increased pumping capacity of the lift station.

DETAILED DESCRIPTION OF THE DRAWING AND OPERATION These and otherobjects and advantages of the present invention will be more readilyapparent from the following detailed description of the drawing, inwhich the sole FIGURE is a diagrammatic representation of a sewage liftstation having a pneumatic motive fluid system and an electrical motorand control system, and embodying principles of the present invention.

Referring to the FIGURE, a sewage lift station is provided with an inlet11 and an outlet 12. The inlet 11 connects with a sewer at an inletlevel 13 and the outlet 12 connects at an outlet level 14 to a sewagedelivery line (not shown) which conducts sewage to a sewage treatmentplant. The outlet level 14 is at some elevation represented by thedimension line 15 above the inlet level 13. The essential function ofthe lift station 10 is to receive sewage at the inlet port 1 l where itenters by gravity flow, and to discharge it at the outlet 12 at level14, where it can further proceed by gravity flow toward the treatmentstation.

The lift station 10 includes a sewage handling unit 20, a pneumaticmotive fluid system 40 which supplies pressurized air to the unit 20,and an electrical control system 60 which controls and times theoperation of the pneumatic system 40 and thus the sewage handling unitof the lift station 10.

The lift station 10 further includes a wet well 16. The wet well 16 hasan inlet 17 which forms the inlet 11 of the lift station 10, and anoutlet 18 which connects with an inlet 21 of the unit 20. The wet well16 serves as an accumulator tank in which sewage is continuouslyreceived through the inlet 17, into which it flows under its own weight,and from which it flows, also by gravity, to the unit 20 via the wetwell outlet port 18. When the outlet 18 is closed, as it will be, forexample, during a unit ejection cycle as will be explained below, thewet Well 16 accumulates the sewage from the inlet port 11 until suchtime as the outlet port 18 is again opened.

The lift station 10 also includes an outlet sewage line 19 whichcommunicates between an outlet 22 of the unit 20 and the station outletport 12. The outlet line 19 is not physically a part of the lift station10. It is designed to withstand the pressurized output of the sewagehandling unit 20.

Generally, the diameter of the outlet duct 19, as well as the inlet andoutlet ports 11 and 12, the wet well inlet and outlet port 17 and 18,and the unit inlet and outlet ports 21 and 22, must be of a diameter ofusually four inches or more, in order to accommodate sewage which maycontain solid particles of several inches in diameter. Accordingly, theinternal sewage transmitting passages of the unit 20 must be of asimilarly large diameter.

The sewage handling unit 20 is the sewage displacing portion of the liftstation 10. It includes a conduit 23 which is connected through a checkvalve 24 to the unit inlet 21, and through a check valve 25 to the unitoutlet 22. Connected between the check valves 24 and 25 in the duct 23is a T 26. The T 26 has a side port connecting to a vertical duct 27,which connects through the mouth 28 in the top of a sewage receiver tank30 to the tank interior. Of the components of the lift station 10, thetank 30 is physically located at the lowest level in most cases. Thepneumatic and electrical control systems 40 and 60 are usually housedjust above or below ground level at the lift station location. Theextension of the vertical duct 27 inside the tank 30 com municates witha region 32 near the bottom of the tank 30. Connected near the top ofthe tank 30 on the inside thereof, is a liquid level sensing switch 34which is at a vertical level 35 below the level of the output port 18 ofthe wet well 16. The mouth 33 of the vertical duct 27 is located at alevel 36 at some distance 37 below the level 35, and at some distance 38below the output level 12. At the top of the tank 30 is provided an airport 39. The tank 30 is essentially airtight except for the ports 28 and39. Sewage accumulates and is ejected from the tank 30 through the port28. Air is vented from the tank 30, while sewage is accumulating in thetank, and is injected into the tank 30 under pressure to force sewagefrom the tank 30 through the port 39.

The pneumatic system 40 is provided with a port 41 which connectsthrough a line 42 to the air port 39 of the tank 30, and with a ventport 54 which communicates with the atmosphere. A three-way solenoidcontrolled valve 43 is provided to selectively connect the port 41alternatively to the exhaust port 54 and a pressurized air supply line44. When the solenoid 43' of the solenoid valve 43 is de-energized, theport 41 is normally connected to the exhaust port 54 while the supplyline 44 is blocked. When the valve solenoid 43' is energized, the port41 communicates with the air supply line 44 and the exhaust port 54 isblocked. Preferably, the exhaust port 54 is vented through the wet wellto reduce noise and confine odors.

A compressor 45 is provided having an inlet port 46 connecting toatmosphere and an outlet port 47 connecting through a pressure releasesafety valve 48 to an air delivery line 49. The air delivery line 49connects to the mouth 50 of an accumulator tank 51, .and through apressure regulator valve 52 to the air supply line 44. The valve 52maintains the air to the supply line 44 from the accumulator tank 51 orthe compressor 45 at a constant pressure.

The electrical control circuit 60 includes a timer 61 having an input 62connected to the level sensor switch 34 of the tank 30, and an output 63connected to the winding 43 of the solenoid valve 43. The timer 61 isenergized by a signal from the level sensor 34 whenever the level in thetank 30 has reached the level 35, to activate the solenoid 43' for afixed period of time. The control 60 also includes an electric motor 66having an output shaft connected to the drive shaft 67 of the compressor45 so as to drive the compressor. The motor 66 is illustrated as aone-phase AC electric motor provided with leads 68 which are connectedthrough the contacts 69 of a starter assembly 70 to a one phase AC powersource 71. The starter assembly 70 includes the sets of normally openedswitch contacts 69 connected in series with the leads 68 of the motor66. The starter further includes an actuator 74 which operates to closethe contacts 69 when energized. The actuator 74 is provided with aninput 75 which is connected to a pressure switch 76 in the accumulatortank 51 which energizes the winding 74 to close the contacts 69 when thepressure' switch is activated. The pressure switch 76 activates when thepressure in the tank 51 falls below a minimum pre-set pressure tothereby energize the winding 74 to turn on the compressor motor 66. Whenthe pressure has reached a prescribed maximum value, another pressureswitch 78 is provided at the accumulator tank 51 which is connected toanother input 79 of the winding 74 so as to de-energize the winding 74to turn off the motor 66 and the compressor 45. Thus, the starter switch70 acts as a conventional double-acting relay. The starter assembly 70also includes overload protection (not illustrated) to de-energize therelay 74 if the motor is overloading the power lines 68.

In some systems, a second back-up compressor is provided to operate ifthe first compressor were to fail. In such a case, a third sensor wouldbe provided to start the second compressor rather than the sensor 76.This sensor would be set to a pressure below that of the sensor 76, tostart the second compressor if the first compressor fails to keep theaccumulator pressure at an adequate level.

In operation, sewage enters the inlet port 11 at the inlet level 13 andflows under the force of gravity through the wet well 16, through theoutlet of the wet well 18 to the inlet port 21 of the unit 20. Thesewage proceeds under the force of gravity through the check valve 24 tothe line 23 and into the sewage port 28 of the receiver tank 30. Thesewage will continue to accumulate in the tank 30 in this manner untilthe level in the tank 30 has reached the level 35 of the sensor switch34. When the sewage has reached this level 35 to trip the level sensorswitch 34, a sewage ejection cycle is initiated in which air underpressure is injected into the receiver tank 30 through the air port 39to force the sewage out of the tank 30 through the duct 27. Thispressure in the line 23 causes a check valve 24 to close and the checkvalve 25 to open as the sewage is ejected from the tank through theoutput port 22 of the pump 20, and into the outlet line 19 toward theoutlet port 12 at the level 14.

At the end of the ejection cycle, the air pressure is relieved throughthe air port 39 and the sewage from the ou'tp'ut line 19 will tend toflow backward toward the tankunderthe influence of gravity, causing thecheck valve 25to close, trapping the ejected sewage in the outletline19. At the end of this ejection cycle, the sewage level at thereceivertank 30 is at the level 36 adjacent the'mouth 33 of the duct 27.During the ejection cycle, while the check valve 24 is closed, thesewage has accumulated in-the wet well 16. When the pressure is relievedfrom the tank 30 at the end of the ejection cycle, this sewage in thewet well forces open the check valve 24 and proceeds to accumulate inthe receiver tank 30 and the next cycle proceeds in the manner set forthabove.

During the ejection cycle, the air pressure injected into the receivertank 30 through the port 39 acts directly on the sewage liquid withinthe tank 30 to force it up through the duct 27 toward the outlet port 12at the level 14. To force the sewage out of the tank 30, air pressureequal to or greater than the hydrostatic pressure caused by sewagestanding in the duct 27 and output line 19 equal to a height 38 betweenthe levels 36 and 14 is required. Normally, a slightly greater pressure'is' desired to accelerate the ejection cycle; however, ex-

cessive ejection pressures are preferably avoided in order to prevent anexcessive loss of power due to the dynamic losses of the sewage movingthrough the sewage lines at high velocities.

The ejection cycle is controlled by the timer 61 and the valve 43. Whensewage is accumulating in the tank 30, the valve 43 is de-energizedconnecting the air port 39 with atmosphere through the line 42 and theexhaust port 54 of the valve 43. At the start of an ejection cycle, thesewage at the level 35 trips the level sensing switch 34 to energize thetimer 61. 'Once the timer is energized, an electrical signal is producedon line 63. This signal has a fixed duration which energizes thesolenoid 43' of the valve 43 for a fixed period of time. This feeds airfrom the accumulator tank 51 through the pressure regulator valve 52through the valve 43 and the line 42 into the tank 30 at a constantpressure through the air port 39. Ideally, the valve 43 remains open fora period of time long enough to obtain a pump displacement which causesa reducing of the sewage level in the tank 30 from the level 35 to thelevel 36, during an ejection cycle. Typically, this'displacement isdetermined by the volume to which the injected air has attained when itis fully expanded in the sewage receiver tank. The setting of the timer61 which is required to most effectively achieve this is best determinedby experimentation. Generally, the time required will vary with thedifferent systems and plumbing configurations employed. Importantconsiderations are the dynamic losses and the hydrostatic pressure atthe mouth 33 of the duct 27.

The setting of the timer 61 and the pressure regulator valve 52 aremutually dependent. A higher pressure setting on the valve 52 requires ashorter time setting on the timer 61. Thisrelationship is notnecessarily a linear relationship in order to maintain a givendisplacement of the pump 20. Instead, the relationship might vary withpressure for some systems due primarily to the effects of dynamic forcesinvolved in accelerating the fluid out of the tank 30 and due to thedynamic losses caused by the moving fluid through the sewage lines.

The combination of the regulator 52 and the timer 61 provides a meansfor regulating the quantity "of injected air and thus the displacementof the pump during each ejection cycle and maintaining itconstantfromcycle to cycle. In this manner, the displacement of eachinjection cycle is optimized, thereby eliminating the waste of air byusing air in excess of receiving tank capacity, and also preventing aloss in the overall lift station capacity by using less air than thereceiver tank capacity.

The air pressure supplied through the regulator 52 is supplied from theair accumulator 51 where air is stored at a pressure which is maintainedabove the pressure setting of the regulator 52. This pressure is somaintained above a prescribed minimum level by the setting of thepressure sensing switch 76. When the air pressure falls below thispre-set level of the switch 76, an electrical signal is generated on theline 75 to energize the starter actuator 74. This closes the set ofswitch contacts 69, turning on the compressor motor 66 which drives thecompressor 45 to pump air from the atmosphere port 46 into theaccumulator 51. At some maximum pressure as set by the sensing switch78, an electrical signal is generated on the line 79 to de-energize thestarter actuator 74, breaking the contacts of the switch 69, turning.off the motor 66 and the compressor 45. The number of stops and startsof the motor 66 determines the service life of the starter 70 and themotor 66. This number of stops and starts is primarily determined by theamount of air used in each ejection cycle, and the amount of air storedin the accumulator 51. In this respect, it is desirable to use a minimumamount of air in each ejection cycle, while storing a maximum amount ofair in the accumulator 51. The amount of air stored in the accumulator51 is determined by the size of the accumulator 51 and the pressuredifference between the maximum and minimum pressures as determined bythe pressure sensor switches 76 and 78.

Also, the overall power efficiency of the system is greater when themotor 66 is run at a continuous speed than it is when it is beingstopped and started frequently. In this respect, it is desirable toselect a wide range between the minimum and maximum pressures in theaccumulator 51. The pressure regulator 52 permits usage of greaterpressure differential between the maximum and minimum pressures of theaccumulator 51 while maintaining constant pump displacement from cycleto cycle. For example, the minimum pressure as set by the sensing switch76 is maintained at, say, 3 psi above the setting of the regulator 52,while the maximum pressure set by the sensing switch 78 is maintained ashigh as possible but within the pressure ratings of all of thecomponents which are subject to high pressure. The regulator 52, on theother hand, is set for the best efficiency considering the dynamic headand other factors of the system.

Furthermore, the motor operates more efficiently if his being operatedat a relatively high optimum speed under an optimum load. The optimumspeed and load are different for different compressor-motorcombinations. Because the motor starts less and runs longer, more workis done when the motor is running under opti'mum load.

advantage of providing a pressure regulator is that the pressure sensor76 can be set enough above the setting of the pressure regulator 52 sothat, in a given ejection cycle, the pressure of the accumulator 51 willnot drop below the setting of the pressure regulator 52.

If this occurs, the pump displacement and lift station capacity will bereduced. In such a case, the compressor motor 45 cannot supply enoughair to maintain the regulator pressure, and the pump displacement willdrop below the receiver tank capacity, decreasing the effective capacityof the lift station. Furthermore, be cause the tank would not becompletely evacuated, it would fill faster, and when the sewage flowrate is high, this may occur before the compressor can charge theaccumulator to adequate pressure to empty the receiver in the nextejection cycle.

Therefore, the present invention provides for increased lift stationcapacity particularly when this capacity is most needed, in cases ofhigh sewage flow.

What is claimed is: 1. An air lift station for receiving sewage from aninlet at a first level and for delivering said received sewage to anoutlet at a second level at a higher elevation than said first level, byintermittently ejecting said received sewage toward said outlet indiscrete ejection cycles with controlled blasts of pressurized air, saidstation comprising:

a sewage receiver having means for communicating sewage to said receiverfrom said inlet, and means for communicating sewage from said receiverto said outlet; means for supplying pressurized air to said receiver ateach ejection cycle, said air supplying means including: an airaccumulator for storing air under pressure, a fluid path connecting saidaccumulator with said receiver,

valve means in said fluid path for selectively opening said path duringsaid ejection cycles and closing said path between said ejection cycles;

an air compressor for supplying pressurized air to said accumulator,said compressor having an outlet connecting with said air accumulator;

means for intermittently driving said compressor in discrete compressioncycles, said driving means including an electric motor and selectivelyoperable circuit means for connecting said motor to a source ofelectrical power; and

means for controlling the injection of air to said receiver in aplurality of ejection cycles between each of said compression cycles soas to maximize the number of ejection cycles per each compression cycle,said control means including means for maintaining the quantity of airinjected into said receiver approximately constant from cycle to cyclecomprising:

a. regulator means connected in said fluid line between said accumulatorand said receiver, and

b. timing means operable to open said valve means for an interval thatis approximately constant from cycle to cycle.

2. An air lift station according to claim 1 wherein:

said regulator means in a pressure is effective to control the pressureof the air injected into said receiver in the same manner during each ofsaid ejection cycles.

3. An air lift station according to claim 2 wherein:

said pressure regulator means is effective to maintain a constantpressure of the injected air throughout each ejection cycle.

4. An air lift station according to claim 1 wherein:

said regulator is a flow regulator effective to control the flow rate ofthe air into said receiver in the same manner during each of saidejection cycles. 5. An air lift station for receiving sewage from aninlet at a first level and for delivering said received sewage to anoutlet at a second level at a higher elevation than said first level, byintermittently ejecting said received sewage toward said outlet indiscrete ejection cycles with controlled blasts of pressurized air, saidstation comprising:

a sewage receiver having means for communicating sewage to said receiverfrom said inlet, and means for communicating sewage from said receiverto said outlet; means for supplying pressurized air to said receiver ateach ejection cycle, said air supplying means including: an airaccumulator for storing air under pressure, a fluid path connecting saidaccumulator with said receiver,

valve means in said fluid path for selectively opening said path duringsaid ejection cycles and closing said path between said ejection cycles;

an air compressor for supplying pressurized air to said accumulator,said compressor having an outlet connecting with said air accumulator;

means for intermittently driving said compressor,

said driving means including an electric motor and selectively operablecircuit means for connecting said motor to a source of electric power;

means for controlling the injection of air to said receiver during eachof said ejection cycles to maintain the quantity of the air injectedinto said receiver tank constant from cycle to cycle;

a first pressure sensor in said accumulator for generating a firstsignal when the pressure in said accumulator falls below a predeterminedminimum value;

a second pressure sensor in said accumulator for gen erating a secondsignal when the pressure in said accumulator rises above a predeterminedmaximum value;

said circuit means being operative to connect said motor in response tosaid first signal and to disconnect said motor in response to saidsecond signal; and

said control means including a pressure regulator for maintaining theair injected into said receiver at a pressure which is less than saidpredetermined minimum pressure of said accumulator but greater than thehydrostatic pressure at said receiver of sewage moving toward saidoutlet.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN PATENT NO. 2 3 915593 DATED October 28, 1975 |NVENTOR(S) Jess L. Chamberlain It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 40, "that" should be than-.

Column 2, line 46, delete the word "the" (second occurrence) Column 8,line 59, Claim 2, delete "in a pressure is" and insert -is a pressureregulator.

Signed and Scale this Tenth Day of August 1976 (SEAL! Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parentsand Trademarks

1. An air lift station for receiving sewage from an inlet at a firstlevel and for delivering said received sewage to an outlet at a secondlevel at a higher elevation than said first level, by intermittentlyejecting said received sewage toward said outlet in discrete ejectioncycles with controlled blasts of pressurized air, said stationcomprising: a sewage receiver having means for communicating sewage tosaid receiver from said inlet, and means for communicating sewage fromsaid receiver to said outlet; means for supplying pressurized air tosaid receiver at each ejection cycle, said air supplying meansincluding: an air accumulator for storing air under pressure, a fluidpath connecting said accumulator with said receiver, valve means in saidfluid path for selectively opening said path during said ejection cyclesand closing said path between said ejection cycles; an air compressorfor supplying pressurized air to said accumulator, said compressorhaving an outlet connecting with said air accumulator; means forintermittently driving said compressor in discrete compression cycles,said driving means including an electric motor and selectively operablecircuit means for connecting said motor to a source of electrical power;and means for controlling the injection of air to said receiver in aplurality of ejection cycles between each of said compression cycles soas to maximize the number of ejection cycles per each compression cycle,said control means including means for maintaining the quantity of airinjected into said receiver approximately constant from cycle to cyclecomprising: a. regulator means connected in said fluid line between saidaccumulator and said receiver, and b. timing means operable tO open saidvalve means for an interval that is approximately constant from cycle tocycle.
 2. An air lift station according to claim 1 wherein: saidregulator means is a pressure regulator effective to control thepressure of the air injected into said receiver in the same mannerduring each of said ejection cycles.
 3. An air lift station according toclaim 2 wherein: said pressure regulator means is effective to maintaina constant pressure of the injected air throughout each ejection cycle.4. An air lift station according to claim 1 wherein: said regulator is aflow regulator effective to control the flow rate of the air into saidreceiver in the same manner during each of said ejection cycles.
 5. Anair lift station for receiving sewage from an inlet at a first level andfor delivering said received sewage to an outlet at a second level at ahigher elevation than said first level, by intermittently ejecting saidreceived sewage toward said outlet in discrete ejection cycles withcontrolled blasts of pressurized air, said station comprising: a sewagereceiver having means for communicating sewage to said receiver fromsaid inlet, and means for communicating sewage from said receiver tosaid outlet; means for supplying pressurized air to said receiver ateach ejection cycle, said air supplying means including: an airaccumulator for storing air under pressure, a fluid path connecting saidaccumulator with said receiver, valve means in said fluid path forselectively opening said path during said ejection cycles and closingsaid path between said ejection cycles; an air compressor for supplyingpressurized air to said accumulator, said compressor having an outletconnecting with said air accumulator; means for intermittently drivingsaid compressor, said driving means including an electric motor andselectively operable circuit means for connecting said motor to a sourceof electrical power; means for controlling the injection of air to saidreceiver during each of said ejection cycles to maintain the quantity ofthe air injected into said receiver tank constant from cycle to cycle; afirst pressure sensor in said accumulator for generating a first signalwhen the pressure in said accumulator falls below a predeterminedminimum value; a second pressure sensor in said accumulator forgenerating a second signal when the pressure in said accumulator risesabove a predetermined maximum value; said circuit means being operativeto connect said motor in response to said first signal and to disconnectsaid motor in response to said second signal; and said control meansincluding a pressure regulator for maintaining the air injected intosaid receiver at a pressure which is less than said predeterminedminimum pressure of said accumulator but greater than the hydrostaticpressure at said receiver of sewage moving toward said outlet.